Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique increasingly used to modulate neural activity in the living brain. In order to establish the neurophysiological, cognitive or clinical effect of tDCS, most studies compare the effects of active tDCS to those observed with a sham tDCS intervention. In most cases, sham tDCS consists in delivering an active stimulation for a few seconds to mimic the sensations observed with active tDCS and keep participants blind to the intervention. However, to date, sham-controlled tDCS studies yield inconsistent results, which might arise in part from sham inconsistencies. Indeed, even if most studies report using similar approaches as described in an early study by Gandiga et al. (2006,) [1Gandiga P.C., Hummel F.C., Cohen L.G. Transcranial DC stimulation (tDCS): A tool for double-blind sham-controlled clinical studies in brain stimulation Clin Neurophysiol 2006 ;  117 (4) : 845-850 [cross-ref]

Cliquez ici pour aller à la section Références], the original protocol (i.e., 10 s ramp-up followed by 30 s of active stimulation at 1mA before manually turning off the stimulator) has been largely modified, adjusting (a) the intensity and duration of active current being delivered (from “no current” to 2minutes at 1mA), (b) the duration of ramp-in and ramp-out phases (e.g. 5–30 s), and (c) the number of ramps done throughout the stimulation. Therefore, this multiplicity of sham stimulation protocols, used in the tDCS research field, might have different biological effects beyond the intended transient sensations. Here, we seek to enlighten the scientific community to this possible confounding factor in order to increase reproducibility of neurophysiological, cognitive and clinical tDCS studies.